This invention relates to a method of recovering hydrocarbons involving a surfactant system derived from lignin products. More particularly, the surfactant system comprises four components: a lignin phenol surfactant, lignin, an amine, and a solubilizer.
Investigations of ways to increase oil recovery by improving the displacement ability of floods have produced useful surfactants which reduce the interfacial tension between the oil and water in the reservoir. With lower interfacial tension, oil that is trapped in the pore structure can disperse into the water as smaller and more easily deformable droplets. Many types of surfactants have been investigated and the choice of which surfactant to employ in a flood operation is dependent upon the conditions in the reservoir, as well as the cost and availability of the surfactants.
Most surfactant floods have employed a petroleum sulfonate as a sole surfactant, or at least a major component of a mixture of surfactants. Synthetic alkylaryl sulfonates and alkyl sulfonates and sulfates have been proposed as oil recovery surfactants. Sulfonates are preferred because they have a better high temperature stability than the sulfates. These surfactants are all classified as organic sulfonates and are usually metal salts of alkylbenzene sulfonate containing 12 to 30 carbon atoms, but may also be aliphatic sulfonates or alkylated naphthalene sulfonates. These surfactants have an equivalent weight that ranges from 320 to 700 g/equivalent.
To combat layering and precipitation problems in high salinity applications, a material with both water-soluble and oil soluble characteristics is usually added to organic sulfonate surfactant mixtures. When used in surfactant flooding, these materials are generally referred to as "solubilizers" or "cosurfactants" and often constitute the most expensive component in a surfactant mixture. Conventional solubilizers are sulfate or sulfonate salts of polyethoxylated alcohols or alkyl phenols. The amount of solubilizer required depends on the amount of and types of organic sulfonate surfactants employed in a surfactant flood operation. A minimum amount of solubilizer is required to prevent the surfactants from precipitating from the flood water. The choice of the solubilizer employed is dependent on the choice of surfactants to be used and the salinity of the flood water. Surfactant quantity is a function of the reservoir's size and other characteristics. The concentration of surfactant components in the system is usually 1% to 6% expressed on an active surfactant basis. The surfactant slug is usually made up in high salinity brine and the customary polymer slug in fresh water.
One problem with many surfactants is their high cost of manufacture. Surfactants which are relatively cheap have an inherent advantage in the market place, especially if the surfactants are to be used in a high volume, enhanced oil recovery application.
One approach taken has been to substitute lignin phenol surfactants for water soluble, petroleum sulfonate surfactants in surfactant flooding systems. This replaces some of the relatively expensive petroleum sulfonates with surfactants prepared from lignin, a low cost material. In U.S. Pat. Nos. 4,739,040 and 4,787,454, the preparation of surfactants from lignin and their use in surfactant flooding systems is discussed. These patents disclose reducing lignin in the presence of a carbon monoxide or hydrogen reducing agent at high temperature and pressure to produce low molecular weight lignin phenols, and transforming the lignin phenols to surfactants by one or a combination of several reactions such as alkoxylation, alkylation, sulfonation, sulfation, alkoxysulfation, and sulfomethylation.
Another approach has been to develop a lignin amine surfactant system wherein high equivalent weight, oil soluble, petroleum sulfonate surfactants are replaced with lignosulfonate and an amine. U.S. Pat. Nos. 4,756,370 and 4,821,803 discuss such lignin amine surfactant systems which contain less of the more expensive petroleum sulfonates and more lignin products.
A third approach of substituting lignin products for expensive petroleum sulfonate surfactants is disclosed in U.S. Pat. No. 4,548,721. This reference discloses the use of the reaction product of a lignin and an amine at elevated temperatures as an enhanced oil recovery surfactant.